Fluorescein | CAS 2321-07-5 | ≥90% Dye Content

Technical Specifications

Product Description & Scientific Applications

Fluorescein (3',6'-dihydroxyspiro[2-benzofuran-3,9'-xanthene]-1-one; resorcinolphthalein; C.I. Solvent Yellow 94; D&C Yellow No. 7) is a synthetic xanthene dye and among the most widely used fluorophores in biological and analytical research. In water it absorbs maximally near 494 nm and emits bright green fluorescence near 521 nm, with strongly pH-dependent spectra (pKa ≈ 6.4) and an isosbestic point at 460 nm. It is the parent fluorophore of the amine-reactive labels fluorescein isothiocyanate (FITC) and NHS-fluorescein, and of the 6-FAM phosphoramidite used to tag synthetic oligonucleotides.

Common Scientific Applications

• Fluorescent labelling and bioimaging (FITC, NHS-fluorescein, 6-FAM): Fluorescein-derived reactive labels such as FITC and NHS-fluorescein conjugate to primary amines on proteins, antibodies, and cellular components for immunofluorescence and immunoassays, while the 6-FAM phosphoramidite tags synthetic oligonucleotides for qPCR probes and sequencing. Fluorescein-labelled molecules also act as tracers in cells and tissues.
• Flow cytometry: FITC excites efficiently at the 488 nm line of argon-ion and solid-state lasers, serving as a standard fluorophore for cell staining and sorting and as an anchor channel in multicolour cytometry panels.
• Fluorescence quantum-yield standard: In 0.1 M NaOH, fluorescein is a long-standing quantum-yield reference for calibrating fluorescence spectrometers and for determining the quantum yields of new fluorophores by comparative methods.
• Analytical indicator: Acts as an adsorption indicator in argentometric (Fajans) halide titrations, and detects soluble hydroxides, carbonates, and ammonia through the intense green fluorescence it develops in alkaline media, down to trace levels.
• Hydrological and environmental tracing: A highly detectable, water-soluble tracer for groundwater-flow studies, hydraulic-connection mapping, and leak detection, including hydrostatic and subsea oil-and-gas pipeline leak testing, traceable at very low concentrations over long distances.
• Forensic detection of latent blood: Reveals dilute or latent bloodstains by the fluorescence it produces under appropriate illumination, used alongside chemiluminescent methods such as luminol in crime-scene work.
• Synthetic precursor to halogenated xanthene dyes: Brominated to give the dye eosin Y, and the parent scaffold of halogenated xanthene dyes such as erythrosine and Rose Bengal.
• Dye-laser gain medium: Lases in the green–yellow region as a classic tunable organic dye-laser medium.
• ORAC antioxidant-capacity assay: Serves as the fluorescent probe whose emission decays under a peroxyl-radical flux; antioxidants slow the decay, giving a quantitative measure of antioxidant capacity.

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